This invention relates to the production of and use of thermoplastic polymeric foamed particles as controlled release compositions for use in controlled release devices for controlled release of diagnostic materials and/or insect repellents and/or animal repellents and/or aroma augmenting or enhancing compositions. The process for producing such foamed particles containing such functional fluids or solids involves the use of a single screw or twin screw extruder and placing the resin, functional fluid or solid and gaseous or liquid blowing agent into the extruder stream at specific ranges of lateral intervals.
An ever increasing requirement in the medical diagnosis field as well as in the perfume, animal repellent and insect repellent industries exists for a slow controlled release device for slowly and controllably releasing diagnostic compositions for diagnosing physiological malfunctions or aberrations in mammalian species, animal repellents, insect repellents and/or perfume materials into a gaseous environment in order to aid in the diagnosis of such malfunctions or aberrations and/or to aesthetically scent the said environment and/or in order to repel insects and/or in order to repel mammalian species, e.g. deer, coyote, dogs and the like.
Slow release polymers containing perfumes are well known in the prior art. Thus, United Kingdom Patent Specification No. 1,589,201 assigned to Hercules, Inc. discloses a thermoplastic resin body consisting of a thermoplastic polymer of ethylene and 6-60 weight percent of a polar vinyl monomer selected from the group consisting of vinyl acetate, methyl acrylate, ethyl acrylate, butyl acrylate and acrylic acid wherein the perfumed resin body is suitable for the preparation of shaped objects from which perfume odor emanates over a prolonged period at a stable level.
U.S. Pat. No. 3,505,432 discloses a method of scenting a polyolefin which comprises:
(a) mixing a first amount of liquid polyolefin, e.g. polyethylene or polypropylene with a relatively large amount of scent-imparting material to form a flowable mass;
(b) forming drops from said mass and causing substantially instantaneous solidification of said drops into polyolefin pellets having a relatively large amount of scent-imparting material imprisoned therein;
(c) melting said pellets with a second amount of said polyolefin, said second amount being larger than said first amount; and
(d) solidifying the melt of (c).
U.S. Pat. No. 4,247,498 issued on Jan. 27, 1981 discloses microporous polymers which are capable of containing volatile substances such as perfumes and the like in forms ranging from films to blocks in intricate shapes from synthetic thermoplastic polymers such as olefinic, condensation or oxidation polymers. In one embodiment of U.S. Pat. No. 4,247,498 the microporous polymers are characterized by relatively homogeneous three-dimensional cellular structure having cells connected by pores of smaller dimension. Also disclosed in U.S. Pat. No. 4,247,498 is a process for making microporous polymers from such thermoplastic polymers by heating a mixture of the polymer and a compatible liquid (e.g., a perfume substance or the like) to form a homogeneous solution, cooling said solution under non-equilibrium thermodynamic conditions to initiate liquid-liquid phase separation, and continuing said cooling until the mixture achieves substantial handling strength. Also disclosed in said U.S. Pat. No. 4,247,498 are microporous polymer products which contain relatively large amounts of such functionally useful fluids as perfume compositions and behave as solids.
U.S. Pat. No. 4,156,067 issued on May 22, 1979 discloses polyurethane polymers characterized by a molecular weight of above 6,000 and having lactone groups and hydroxyl groups in the polymer backbone being prepared by reacting a mixture of polyols, a polyfunctional lactone (e.g. epsilon caprolactone) and a polyfunctional isocyanate proportioned so as to provide certain desired polymer properties. It is indicated in said U.S. Pat. No. 4,156,067 that the product is soluble in alkaline solutions and may be used for light sensitive photographic layers on films, paper or glass; in drug delivery systems, as burn dressings, in body implants such as vascular prosthesis, in molding compositions, and in the manufacture of catheters as well as in delivery of perfume compositions in a slow release manner. It is further indicated in said U.S. Pat. No. 4,156,067 that the water absorptivity of the polyurethane/lactone polymers is above 10%, preferably in the range of about 20% to 60%, and these polymers may range in their physical properties from rigid solids to completely gel-like high water absorptive polymers. It is further indicated in said U.S. Pat. No. 4,156,067 that the polymers provide a leachable substrate wherein the leaching agent may be water, gases, alcohols, esters and body fluids, e.g. animal or human.
Extrusion of thermoplastic foams is well known in the prior art. Thus, the Modern Plastics Encyclopedia (published by the McGraw-Hill Publishing Company) 1982-1983 edition at pages 274 and 275 discloses a section authored by Fred Schrafft entitled "Extruding Thermoplastic Foams". Said article on pages 274 and 275 is incorporated herein by reference. It is indicated therein that three different processes are used for the extrusion of thermoplastic foams:
(i) extrusion of expandable beads PA1 (ii) extrusion of thermoplastics containing a chemical blowing agent and PA1 (iii) direct gas extrusion process. PA1 "the amount of blowing agent can vary widely depending on the resin and the type of product desired. However, generally about 7% blowing agent produces a product of about 5.6 lbs/cu. ft. while 18% blowing agent produces a product of about 1.9 lbs/cu. ft. . . . "
It is further indicated in the Schrafft article that the extrusion using a chemical blowing agent may be carried out on a normal single screw extruder and the direct gas extrusion process may be carried out on single and twin screw extruders. It is further indicated in the Schrafft article that common blowing agents used in the process are hydrocarbons such as pentene or fluorocarbons such as 11, 12 and 114. It is further stated that:
U.S. Pat. No. 3,755,208 (the specification for which is incorporated by reference herein) discloses a process for avoidance of cell collapse in an extrusion process for a copolymer based on a low molecular weight alpha olefin and polar vinyl monomer whereby there is incorporated into the polymer a small amount of partial ester of a long chain fatty acid and a polyol. Federal Republic of Germany Pat. No. 1,520,790 discloses expandable polystyrene beads incorporating polyethylene or polypropylene whereby the expandable polystyrene beads are prepared by aqueous suspension polymerization of styrene with the addition of a vaporizable blowing agent, the polymerization being carried out in the presence of from 0.01 up to 1.0 weight percent polyethylene or polypropylene having a molecular weight of less than 4,000. The publication date of this German patent is May 30, 1973.
Foamable styrene polymers are indicated to be prepared according to U.S. Pat. No. 3,758,425, the disclosure of which is incorporated by reference herein. In U.S. Pat. No. 3,758,425 a process is disclosed for preparing foamable styrene polymer beads containing blowing agents with a particularly favorable narrow grain size distribution, the process comprising the use of copolymers of N-vinyl-N-alkyl acetamide having from 1 to 4 carbon atoms in the alkyl group with an ester of acrylic, methacrylic, malaic or fumaric acid with an aliphatic alcohol having a linear or branched chain and containing from 6 to 18 carbon atoms, as protective colloid in the homo- or copolymerization of styrene in an aqueous suspension in the presence of a blowing agent.
U.S. Pat. No. 3,759,641, the disclosure of which is incorporated by reference herein, as well as U.S. Pat. No. 3,577,360, the disclosure of which is incorporated by reference herein, discloses a process and apparatus for pre-expanding polymer particles to a predetermined density which particles are subject to further expansion. Thus, there is disclosed agitated particulate expandable polymer which is heated in a dry atmosphere in a closed vessel, under vacuum, to a predetermined density. To achieve ultra-low density expandable prepuff, a coolant such as water is introduced into the closed vessel after the predetermined density is reached, but prior to the release of the vacuum. Following release of the vacuum, the beads are removed from the closed vessel and may be molded directly without any aging period such as that necessary following steam pre-expansion.
German Pat. No. 1629296 published on Feb. 20, 1973, the disclosure for which is incorporated by reference herein, discloses the production of particles of foam polyethylene by exposure to an inert gas whereby the density is reduced. Thus, particles of closed cell film polyethylene are obtained by extruding an ethylene polymer in the presence of a foaming agent, e.g. isobutane. After extrusion, the product is exposed to an inert gas under high pressure at up to 20.degree. C. below the melting point of the polymer. The inert gas has a permeability coefficient equal to or less than that of air.
U.S. Pat. No. 3,067,147 issued on Dec. 4, 1962 (Rubens, et al) assigned to Dow Chemical Company discloses the use of 1,2-dichlorotetrafluoroethane which can be injected into polyethylene during extrusion to produce an extruded gel which spontaneously expands as it is extruded into a reduced pressure. A special technique, such as cooling, has been used to produce a stable polyethylene foam as disclosed in said U.S. Pat. No. 3,067,147, the specification for which is incorporated by reference herein. The Rubens, et al patent describes an extrusion process for producing low density (0.04 grams/cm.sup.3) polyethylene foams. The variables that influence the mechanical properties of these materials are disclosed in Rubens and Skochdopole in J. Cellular Plastics, January 1965 at pages 91-96, the disclosure of which is incorporated herein by reference.
As disclosed at page 269 of the text "Plastic Foams: the physics and chemistry of product performance and process technology", Volume 1: Chemistry and Physics of Foam Formation, author: Calvin J. Benning published by Wiley-Interscience, a division of John Wiley and Sons, N.Y., (copy in U.S. Patent and Trademark Office Scientific Library), a process for continuous extrusion of expansion of medium density (20-30 lbs. per cu. ft.) polyethylene and sheet has been commercialized by the Nippon Art Paper Company of Japan. The process consists of three steps:
1. preparing pellets impregnated with a foaming agent in solution;
2. feeding the coated pellets into the extruder;
3. extruding into the desired shape.
The key to the development of the Nippon Art Paper Company process is the use of polyethylene "expandable" pellets which can be converted into film or sheet on standard polyethylene blown-film equipment. The pellets can also be blow-molded into bottles or tubes. It is further indicated in the Benning textbook that polyethylene foamed sheet has entered such markets as greenhouse insulation, tablecloths, bags, synthetic leather, wallpaper, tents, toys and packaging.
Other "ethafoam" patents whereby expanded extruded foamed polyethylene having a cell size of 0.5-1.0 mm are indicated to be produced are set forth in Rubens, et al. U.S. Pat. Nos. 2,948,664 and Rubens, et al. 2,948,665, the disclosures for which are incorporated by reference herein.
Additional details concerning methods for producing various foams of various dimensions in various polymers are set forth in Benning "Plastic Foams: the physics and chemistry of product performance and process technology/Volume II: Structure Properties, and Applications", author: Calvin J. Benning, Wiley-Interscience a division of John Wiley and Sons, N.Y., copyright 1969 (copy available in United States Patent & Trademark Office scientific library), the disclosure of which is incorporated by reference herein. Of particular importance are the following pages in the Benning texts:
Volume I: pages 261-344 inclusive
Volume II: pages 20-25, 80-85, 90-93.
U.S. Pat. No. 2,860,377 issued on Nov. 18, 1958 (Bernhardt and Whitfield) discloses the production of a foamed polyethylene by dissolving a gas such as nitrogen therein at elevated pressure while the said plastic is being advanced through an extruder barrel by the action of a rotating extrusion screw, and thereafter releasing the plastic through a die whereby a plastic foam is produced.
In U.K. Patent Specification No. 1,044,397 published on Sept. 28, 1966, it is disclosed that as blowing agents for making foamed polyolefins, it is possible to employ all conventional inorganic and organic compounds which evolve a blowing gas, e.g. nitrogen or carbon dioxide, and it is further disclosed that the polyolefins to be foamed according to the invention have blowing agents which are known per se and, optionally, dyestuffs and/or pigments incorporated therein.
Nothing in the prior art, however, discloses the advantages of the simultaneous foamed pellet/functional fluid or solid imparting of the process of our invention.